The present invention relates to a spread spectrum (SS) radio transmission digital mobile communication device such as a spread spectrum radio transmitter and receiver used in digital cellular communication.
In the land mobile communication, there are a plurality of propagation paths from a transmitting point to a receiving point, and a received wave is a synthesized wave composed of a plurality of waves with different propagation paths. For this reason, radio waves transmitted from a transmitting point at the same time are turned to a plurality of signal waves, which are propagated through a plurality of paths. As a result, these waves reach at a receiving point with some deviation over time, and they reach the receiving point while interfering with each other. To eliminate this, path separation is performed by utilizing property of data diffusion in the spread spectrum radio transmission, and the separated signals are synthesized and path synthesizing gain is obtained to improve the receiving characteristics.
In a conventional type spread spectrum radio transmitter and receiver having RAKE receiving functions to eliminate the influence of multi-path as described above comprises, as shown in FIG. 22, a receiving antenna unit 2201, a high frequency unit 2202 for converting a signal received by antenna to a signal of intermediate frequency band, an orthogonal detection unit 2203 for picking up baseband signal from signals of intermediate frequency band, and a RAKE receiver 2210 for carrying out signal processing to eliminate influence of multi-path. The RAKE receiver 2210 comprises an inverse diffuser for performing inverse diffusion to the received signals, delay adjusters 2212-1 to 212-K for adjusting time delay of the signal obtained by path separation, amplification factor variable amplifiers 2213-1 to 2213-K, a propagation path coefficient controller 2214 for controlling amplification factor of each of the amplification factor variable amplifiers 2213-1 to 2213-K, and a RAKE receiving unit adder 2215 for synthesizing signals of each path. In the present application, the terms xe2x80x9cantennaxe2x80x9d and xe2x80x9cadaptive antennaxe2x80x9d are applied to those of general concept, while the terms xe2x80x9cantenna unitxe2x80x9d and xe2x80x9cadaptive antenna unitxe2x80x9d indicate concrete components respectively.
In a conventional type receiving device, radio wave is received first by the receiving antenna unit 2201, and the received signal is converted to a signal of intermediate frequency band by the high frequency unit 2202. The orthogonal detection unit 2203 picks up a baseband signal by orthogonal detection of the signal of intermediate frequency band. The baseband signal is inversely diffused by an inverse diffuser 2211. On the inverse diffuser 2211, inverse diffusion processing practiced in CDMA (Code Division Multiple Access) is performed, i.e. correlative processing is performed for the received signal and diffusion signal, and only highly correlative components of the received signal are left, and delayed wave having delay time greater than chip time width of diffusion signal is detected. Then, at the delay adjuster 2212-m, delay time is compensated and unnecessary signals are removed according to delay time. Phase adjustment by such signal processing and processing of the phase not adjusted here in the subsequent stage by an amplifier are generally practiced in RAKE receiving. The amplitude of output of the phase adjustment delay adjuster 2212-m is adjusted at the amplification factor variable amplifier 2213-m for each of path xe2x80x9cmxe2x80x9d, and path synthesizing is performed at the RAKE receiving device adder. Here, m represents an integer of 1 to K and is also used to indicate one of paths from the first path to the K-th path. At the propagation path coefficient controller, amplification factor of the amplification factor variable amplifier 2213-m is controlled according to the output of the inverse diffuser 2211.
However, in the RAKE receiving unit of the conventional type spread spectrum radio transmission receiving device, signal processing to match multi-path is performed based on the signal after inverse diffusion. Accordingly, processing can be performed on delay wave greater than chip time width of diffusion signal, and it cannot be performed on the delay wave having delay time smaller than chip time width.
Also, in the conventional type spread spectrum radio transmitter and receiver, the smaller the co-channel interference wave (including interference with other station) is, the higher the receiving characteristics are. Therefore, it is necessary to eliminate co-channel interference wave as far as possible.
To solve the above problems, it is an object of the present invention to provide a spread spectrum radio transmission digital mobile communication device having functions of a RAKE receiving unit, by which it is possible to improve receiving characteristics by reducing influence of delay wave having delay time smaller than chip time width of diffusion signal and the influence of co-channel interference wave.
To attain the above object, the spread spectrum radio transmission mobile communication device comprises inverse diffusion means for obtaining correlation of a received signal with a diffusion signal to execute inverse diffusion, and a synthesizing means for synthesizing paths by giving delay time to match the path to the inverse diffusion signal, whereby there are provided a plurality of receiving branches, variable gain amplifying means for adjusting amplification factor of the signal received at each of the receiving branches, adding means for adding the signals outputted from each of the variable gain amplifying means and for inputting them to the inverse diffusion means, and gain control means for controlling amplification of the variable gain amplifying means to reduce influence of delay wave having delay time smaller than chip time width of diffusion signal in the signal inputted to the inverse diffusion means.
According to the present invention, the signal inversely diffused by the inverse diffusion means is processed by path separation, and the synthesizing means synthesizes paths by giving the delay time to match the path to each signal processed by path separation.
Also, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means so that the influence of the delay wave having delay time smaller than chip time width of diffusion signal in the output signal is decreased according to the output signal of the adding means.
Also, in the present invention, there is provided error rate detecting means for detecting error rate of the output of the synthesizing means and the gain control means for controlling amplification factor of the variable gain amplifying means to reduce the error rate.
Also, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to reduce the error rate and to decrease influence of the delay wave having delay time smaller than chip time width of diffusion signal in the output signal of the adding means.
Also, in the present invention, there is provided S/N detecting means for detecting signal power to noise power ratio of the output of the synthesizing means, and the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to noise power ratio.
Further, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to noise power ratio and to decrease influence of delay wave having delay time smaller than chip time width of diffusion signal in the output signal of the adding means.
Further, in the present invention, there is provided S/(N+I) detecting means for detecting a signal power to (noise power+interference power) ratio of output of the synthesizing means, and gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to (noise power+interference power) ratio.
Also, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to (noise power+interference power) ratio and to decrease influence of the delay wave having delay time smaller than chip time width of the diffusion signal in the output signal of the adding means.
Further, in the present invention, there are provided a plurality of combinations of the variable gain amplifying means, the adding means for adding output signals of the variable gain amplifying means, and the inverse diffusion means where signals are inputted from the adding means, and the synthesizing means synthesizes paths by giving delay time to match path to each signal outputted from the inverse diffusion means.
Also, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to decrease influence of delay wave having delay time smaller than chip time width of the diffusion signal in the output signal based on the output signal of the adding means.
Also, in the present invention, there is provided error rate detecting means for detecting error rate of output of the inverse diffusion means, and the gain control means controls amplification factor of the variable gain amplifying means to reduce the error rate.
Further, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to reduce the error rate and to decrease influence of the delay wave having delay time smaller than chip time width of the diffusion signal of the output signal of the adding means.
Also, in the present invention, there is provided S/N detecting means for detecting the signal power to noise power ratio of output of the inverse diffusion means, and the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to noise power ratio.
Further, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to noise power ratio and to decrease influence of the delay wave having delay time smaller than chip time width of the diffusion signal in the output signal of the adding means.
Further, in the present invention, there is provided S/(N+I) detecting means for detecting the signal power to (noise power+interference power) ratio, and the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to (noise power+interference power) ratio.
Further, in the present invention, the gain control means controls amplification factor of the variable gain amplifying means to increase the signal power to (noise power+interference power) ratio and to decrease influence of the delay wave having delay time smaller than chip time width of the diffusion signal in the output signal of the adding means.
Also, in the present invention, there are provided a plurality of the gain control means to match the combination of the variable gain amplifying means, the adding means and the inverse diffusion means, and each of the gain control means independently controls amplification factor of the variable gain amplifying means.
Also, in the present invention, the gain control means is provided one each to a plurality of combinations of the variable gain amplifying means, the adding means and the inverse diffusion means, and the gain control means controls amplification factor of the variable gain amplifying means in each of the combinations so that antenna directivity is dispersed.
As described above, by adding the arrangement of adaptive antenna for controlling directivity of the receiving antenna to a spread spectrum radio transmission digital mobile communication device having functions of a RAKE receiving device, it is possible to decrease influence of co-channel interference wave not properly handled by RAKE receiving functions or influence of the delay wave having delay time smaller than chip time width of the diffusion signal.
In the adaptive antenna, signals of a plurality of receiving branches are amplified by amplification factors under control and are added, and the directivity of the receiving antenna is electrically adjusted. The amplification factor is controlled in such manner that the influence of the delay wave having smaller delay width in the output signal of the adding means is minimized or that error rate of the signals processed by path synthesizing is minimized, or that the signal power to noise power ratio or the signal power to (noise power+interference power) ratio is maximized. Or, based on the influence of the delay wave in the output signal of the adding means and the combination of the error rate and the signal power to noise power ratio or the signal power to (noise power+interference power) ratio, it is adjusted in such manner that these reference values are brought closer to the optimal value. As a result, the influence of the delay wave having delay time smaller than chip time width of the diffusion signal and the influence of the co-channel interference wave are removed from the received signal. The signal is inputted to the inverse diffusion means, and after inversely diffused, the influence of delay wave smaller than the chip time width of the diffusion signal is eliminated by RAKE receiving functions.
In the communication device of the present invention having a plurality of inverse diffusion means and provided with adaptive antenna to control directivity of the signal inputted to each of the inverse diffusion means, it is possible to obtain signal of each path by directivity to a plurality of paths and to increase receiving characteristics by path synthesis of these signals.